1. The Field of the Invention
The present invention is directed generally to a heat exchanger. More specifically, the present invention is directed to a combined gas and water tube heat exchanger for use with a hot water heater.
2. Background Art
Fin-and-tube heat exchangers of conventional hot water systems often include a helical coil tube having fins disposed on external surfaces of the coil tube. Ceramic discs may be utilized to insulate direct heat of a burner from its adjacent components, such as a fan blower and other components disposed at the exhaust of a heat exchanger housing the burner. Typically, a fin-and-tube heat exchanger comprises a generally cylindrical housing, a helix coil tube disposed concentrically inside the housing, a radial-fired burner disposed inside the coil lumen on one end of the helix coil and a ceramic disc disposed inside the helix coil lumen on the opposite end of the helix coil. Typically a top casting fixedly disposed on top of the housing serves as an interface between a fan blower which forces an air/fuel mixture flow to the burner and the burner. The ceramic disc serves as a barrier to shield hot flue gas from damaging components in its path and to channel hot flue gas to more effectively surround the helix coil external surfaces to improve heat transfer from flue gas to the water flowing inside the helix coil.
However, the use of a ceramic disc inside the lumen takes up valuable heat exchanger footprint, increases fabrication and installation costs and fails to harness and recover the maximum amount of energy. In such installations, typically fluid baffle plates are used and positioned between coil windings (loops) such that hot flue gas can be more efficiently directed around coil tube. Though effective in enhancing heat transfer from the hot flue gas to the helix coil, there remain gaps in the path of the hot flue gas to escape through. Poor heat recovery through the top casting further causes an unnecessarily warm top casting, waste to the environment and unnecessarily heats up surrounding components. The construction of fin-and-tube further requires specialized tools to carry out multiple steps involving bending of a tube to create a coil tube and sliding and welding numerous fins over the coil tube to create a good contact of the fins over the coil tube to encourage heat transfer. Significant heat loss also occurs through the heat exchanger housing.
Current heat exchanger designs require insulations on the outer shell of a heat exchanger to prevent heat loss from the heat exchanger to contain heat that would otherwise be lost to the surroundings.
Thus, there arises a need for a heat exchanger capable of harnessing the otherwise damaging or lost heat from the burner and a heat exchanger that is simple and cost effective to fabricate. Further, there is a need to improve the efficiency of a heat exchanger without increasing parts count and the complexity of a heat exchanger.